Soft-magnetic materials used for various reactors, choke coils, pulse power magnetic devices, antennas, cores of transformers, motors and power generators, current sensors, magnetic sensors, electromagnetic wave-absorbing sheets, etc. include silicon steel, ferrite, Co-based, amorphous, soft-magnetic alloys, Fe-based, amorphous, soft-magnetic alloys, and Fe-based, fine-crystalline, soft-magnetic alloys. Though silicon steel is inexpensive and has a high magnetic flux density, it suffers large loss at high frequencies, and is difficult to be made thin. Because ferrite has a low saturation magnetic flux density, it is easily saturated magnetically in high-power applications operable with large magnetic flux densities. Because the Co-based, amorphous, soft-magnetic alloys are expensive and have as low saturation magnetic flux densities as 1T or less, parts made of them for high-power applications are inevitably large, and their loss increases with time due to thermal instability. Though the Fe-based, amorphous, soft-magnetic alloys have as high saturation magnetic flux densities as about 1.5T, they are not sufficient, and their coercivity is not sufficiently low.
On the other hand, the Fe-based, fine-crystalline, soft-magnetic alloys have high saturation magnetic flux densities and excellent soft-magnetic properties. An example of Fe-based, fine-crystalline, soft-magnetic alloys is disclosed in WO 2007/032531. This Fe-based, fine-crystalline, soft-magnetic alloy has a composition represented by the formula of Fe100-x-y-zCuxByXz, wherein X is at least one element selected from the group consisting of Si, S, C, P, Al, Ge, Ga and Be, and x, y and z are numbers meeting the conditions of 0.1≤x≤3, 8≤y≤20, 0<z≤10, and 10<y+z≤24 by atomic %, and a structure comprising crystal grains having an average particle size of 60 nm or less dispersed in a proportion of 30% or more by volume in an amorphous matrix; and having as high saturation magnetic flux density as 1.7 T or more and low coercivity.
This Fe-based, fine-crystalline, soft-magnetic alloy is produced by quenching an Fe-based alloy melt to form an ultrafine-crystalline alloy ribbon comprising fine crystal grains having an average particle size of 30 nm or less dispersed in a proportion of less than 30% by volume in an amorphous matrix, and subjecting this ultrafine-crystalline alloy ribbon to a high-temperature, short-time heat treatment or a low-temperature, long-time heat treatment. The quenched alloy ribbon is peeled from a cooling roll, wound around a reel with its tip end attached thereto, and if necessary, rewound.
Though ultrafine-crystalline alloy ribbons inherently have poor windability because of low toughness and thus easy fracture, they should be wound to a neatly laminated coil shape in mass production. To this end, reels with flanges are used. It has been found, however, that side portions of the ribbon come into contact with flanges of a winding reel in rewinding, making it likely that the ultrafine-crystalline alloy ribbon is frequently fractured. Such problems do not occur in amorphous alloy ribbons having relatively high toughness.